Field of the Invention
The present invention relates to an ophthalmologic apparatus adapted to scan measuring light on the fundus or the anterior ocular segment of an eye to be examined and to image the fondue or the anterior ocular segment, and a control method of the ophthalmologic apparatus.
Description of the Related Art
Among a variety of ophthalmologic apparatuses using optical apparatuses currently in use, an optical coherence tomography apparatus (hereinafter referred to as “the OCT” or “the OCT apparatus”) and a scanning laser ophthalmoscope (hereinafter referred to as “the SLO” or “the SLO apparatus”) have been known. These apparatuses are capable of acquiring the images of a fundus or an anterior ocular segment with a high resolution by scanning measuring light on the fundus or the anterior ocular segment of an eye to be examined and by imaging the light reflected from the eye to be examined. This is making these apparatuses indispensable as ophthalmologic apparatuses.
The OCT apparatus and the SLO apparatus use a galvano scanner or like as a means for scanning measuring light. The galvano scanner is constituted of a mirror fixed to a rotating shaft, an actuator that rotatively drives the rotating shaft, and a driver that drives the actuator. To drive the scanner, an instructed drive position is given to the driver. As an image acquiring means, an avalanche photo diode (hereinafter referred to as “the APD”) or a linear sensor or the like is used. To image the light reflected from an eye to be examined, a synchronizing signal is input to the sensor. The imaging is performed in synchronization with the drive of the scanner.
For example, the OCT apparatus has two scanners, namely, a scanner that scans an eye to be examined in a horizontal direction and a scanner that scans the eye to be examined in a vertical direction. To obtain a single tomographic image with such a configuration, the scanner in the main scanning direction is driven for one line without driving the scanner in the sub scanning direction. Further, a three-dimensional image is obtained by driving the scanner in the sub scanning direction upon the completion of the main scan for one line thereby to shift in the sub scanning direction, thus repeating the main scan for a predetermined number of lines. At this time, in synchronization with the drive start timing of the main scan, the image acquisition is started, and upon the completion of the acquisition for a predetermined number of times of A-scans (the information in the depth direction at one point on an eye to be examined), the image acquisition is stopped.
However, in the actual scanner drive, there is a delay from the issuance of a drive instruction to a scanner until the actual drive position of the scanner reaches an instructed position. Therefore, if the drive start timing and the acquisition start timing are set to be the same, then an image is acquired at a position that is different from a desired position. This results in the occurrence of a positional displacement in the acquired image. A conceivable solution is to wait for a certain time after the drive instruction is issued to the scanner before starting the acquisition, so that an image can be acquired at a desired position. However, the time of the delay varies for each scanner or according to an environmental change or a change over time. For this reason, there has been a demand for measures to securely suppress the occurrence of the positional displacement.
Japanese Patent Application Laid-Open No. 2012-213490 describes an apparatus adapted to acquire an image by taking into account the operational difference between a scan in a forward direction and a scan in a backward direction in a reciprocal scan. However, in the apparatus, the time delay from the issuance of the drive instruction to the actual drive start is not taken into account.
The positional displacement of an image described above may badly affect an image diagnosis by a doctor and may cause the doctor to erroneously identify a lesion, resulting in a misdiagnosis.